#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int DigitSum(unsigned int n)
{
	if (n > 9)
		return (n % 10) + DigitSum(n / 10);
	else
		return n % 10;
}

int main()
{
	int n = 0;
	scanf("%d", &n);
	int sum = DigitSum(n);
	printf("%d", sum);
	return 0;
}